1. Field of the Invention
This invention relates to an optical information medium such as read only optical disk and optical recording disk.
2. Prior Art
Optical materials most typically used for light-transmitting layer and the like of an optical information medium are polycarbonate- and polymethyl methacrylate-based materials in view of their favorable moldability, transparency, price, and the like. These materials, however, suffer from insufficient abrasion resistance, and their high electric insulation invites high susceptibility for electric charge, and a large amount of dust is likely to become attached to the surface of the medium during their storage or use to result in errors in the recording and reading of the optical information.
A countermeasure generally taken for such problem is application of a transparent, scratch-resistant hard coat on the light-transmitting layer of the medium. The process most popularly employed in such case is coating of a curable compound having at least two polymerizable functional groups such as acryloyl group in the molecule on the light-transmitting layer followed by curing with UV or other active energy beam to thereby form a protective layer. Although the protective layer formed from such UV-curable resin may be superior in abrasion resistance compared to the surface of the resin such as polycarbonate or polymethyl methacrylate, the level of the abrasion resistance achieved is limited to a certain level and such level is not the level of the scratch resistance sufficient for use in the optical information medium. In addition, these hard coatings are provided only for the purpose of imparting the surface with the scratch resistance, and a smudge-proof surface which is resistant to attachment of dust or oil mist in the air, fingerprint, and the like is not expectable.
Also proposed is application of a hard coat imparted with anti-static property for prevention of dust attachment as well as sufficient scratch resistance on the substrate on the side of the recording/reading beam incidence. For example, Japanese Patent Application Laid-Open No. (JP-A) 239946/1985 and JP-A 276145/1986 propose addition as an antistatic agent of a cationic amine, an anionic alkylbenzene sulfonate, a nonionic polyol, or ethylene oxide of an alkylphenol, and amphoteric imidazoline or alanine metal salt. JP-A 173949/1991 proposes addition of a lauryl compound, and JP-A 80267/1992 proposes addition of thiocyanic acid and an anionic surfactant containing alkylene glycol chain. These surfactants all have smudge proof effects for inorganic substances such as dust. These methods, however, are substantially ineffective in preventing organic smudges such as fingerprint and oil mist. Furthermore, the surface abrasion resistance of the light-transmitting layer in these proposals is equivalent or inferior to that of the conventional hard coats formed by using a UV-curable resin, and the scratch resistance sufficient for practical use is not at all realized.
A hard coat having smudge-proof properties for organic contaminants is proposed in JP-A 110118/1998 wherein the hard coating material used has a non-crosslinked fluorosurfactant kneaded therein. The hard coat obtained by this method, however, is insufficient in water- and oil-repellency since only a small part of the fluorocompound is exposed to the hard coat surface. When the amount of the fluorosurfactant added to the hard coating material is increased in order to secure sufficient water- and oil-repellent function, the resulting hard coat will suffer from reduced hardness, poor optical properties due to leaching of the excessive surfactant, and handling inconvenience.
As a countermeasure for such problem, JP-A 213444/1999 proposes coating of a fluoropolymer on the surface of the conventional optical disk substrate comprising polycarbonate or the like, and in this application, the water- and oil-repellency is imparted by coating the fluoropolymer on the resin substrate of the optical disk. In contrast to the method wherein a lubricant or the like is kneaded in the hard coating material, the water- and oil-repellent compound of this application is exposed to the entire surface of the hard coat film and sufficient smudge-proof properties are _thereby realized. The fluoropolymer of this method, however, suffers from extremely poor adhesion to the underlying substrate since the fluoropolymer is only physically adsorbed to the underlying substrate by van der Waals force, and the surface treatment with the fluoropolymer is associated with a serious problem of poor durability. JP-A 187663/1994 proposes coating of an acrylic resin surface with a water- and oil-repellent compound by coupling reaction. In this method, a smudge-proof film exhibiting higher adhesion to the underlying surface compared to the JP-A 213444/1999 is provided by coating a water- and oil-repellent compound containing silyl group on the surface of an acrylic resin containing a hydrophilic substituent.
However, the acrylic resins disclosed in the JP-A 187663/1994 are required to contain an adequate amount of hydroxyl group in the polymer chain to thereby enable adsorption of the water- and oil-repellent compound by coupling reaction. This inevitably results in the limited choice of the acrylic resin. In addition, density of the hydroxyl group should be increased to achieve sufficient adhesion between the hard coat surface and the water- and oil-repellent compound, and this may result in the reduced hardness of the hard coat. Alternatively, the hydrophilicity of the hard coat surface may be raised by high energy beam treatment such as plasma or corona discharge treatment. Such treatment, however, is not sufficient in effectively enabling the coupling reaction with the water- and oil-repellent agent, and the satisfactory adhesion is less likely to be achieved solely by this method.
JP-A 203726/1999 discloses a method for improving the scratch resistance of the surface of a resin light-transmitting layer. In this method, two or more inorganic material layers of SiN or SiO are formed by vapor deposition such as sputtering to a total thickness of approximately several hundred nm on the light-transmitting layer comprising a UV-curable resin. However, it is quite difficult to obtain a scratch resistance of practically acceptable level by forming an inorganic film of such thickness.
An object of the present invention is to provide an optical information medium having a light-transmitting layer exhibiting high scratch resistance of practically acceptable level. Another object of the present invention is to provide an optical information medium wherein the light-transmitting layer or the supporting substrate is imparted with smudge-proof properties for organic contaminants such as oil mist and fingerprint (improved readiness for removal of the contaminant) without detracting from the scratch resistance of the light-transmitting layer, and in other words, an optical information medium wherein stable recording/reading is enabled for a prolonged period even if the medium is used as a medium unaccommodated in a cartridge, shell, or caddy, namely, with its surface exposed to contact by fingers and the like. A further object of the present invention is to improve lubricity and durability of the surface on the side of the optical head in a magneto-optical disk used in magnetic field modulation process.
In order to solve the problems as described above, the inventors of the present invention have conducted various investigations for the surface protective layer of the optical information medium. It was then found that it is effective to provide a light-transmitting layer exhibiting excellent scratch resistance comprising a resin and/or a metal (including a semimetal) compound, or hard carbon (DLC) (preferably, separately from the supporting substrate) on the surface of the optical information medium. It was also found that it is effective to provide an underlying layer (which may also function as other constituent member of the medium) exhibiting excellent scratch resistance on the surface of the optical information medium and to further apply a water- and oil-repellent film exhibiting excellent adhesion on the underlying layer.
To be more specific, the present is as described below.
(1) An optical information medium to be optically recorded and/or read, wherein
said medium is coated on at least one surface with a film of a silane coupling agent containing a water- or oil-repellent substituent, said silane coupling agent being represented by the following formula (1):
R1xe2x80x94Si(X)(Y)(Z)xe2x80x83xe2x80x83(1)
xe2x80x83wherein R1 is the water- or oil-repellent substituent; X, Y and Z are independently a monovalent group; and at least one of X, Y and Z is a group which is capable of forming Sixe2x80x94Oxe2x80x94Si bond by polycondensation with silanol group; and
said medium has an underlying layer formed in contact with said silane coupling agent film, and at least the surface of said underlying layer comprises a compound having a chemical bond represented by the formula (2):
Mxe2x80x94Axe2x80x83xe2x80x83(2)
xe2x80x83wherein M is a metal atom (including a semimetal), and A is a chalcogen atom selected from O, S, Se, and Te, nitrogen atom, or carbon atom.
(2) An optical information medium according to the above (1) wherein the surface of the underlying layer coated with said silane coupling agent comprises an active energy beam-curable resin containing a metal (including semimetal) chalcogenide particle, and said metal chalcogenide particle has an average particle size of up to 500 nm.
(3) An optical information medium to be optically recorded and/or read, wherein
said medium is coated on at least one surface with a film of a silane coupling agent containing a water- or oil-repellent substituent, said silane coupling agent being represented by the following formula (1):
R1xe2x80x94Si(X)(Y)(Z)xe2x80x83xe2x80x83(1)
xe2x80x83wherein R1 is the water- or oil-repellent substituent; X, Y and Z are independently a monovalent group; and at least one of X, Y and Z is a group which is capable of forming Sixe2x80x94Oxe2x80x94Si bond by polycondensation with silanol group; and
said medium has an underlying layer formed in contact with said silane coupling agent film, and said underlying layer has a surface comprising a thin layer of a metal (including a semimetal) compound having a thickness of up to 1 xcexcm formed in contact with said silane coupling agent film, and a metal (including a semimetal) compound-containing layer having a thickness thicker than said thin layer is formed in contact with said thin layer and on the side opposite to said silane coupling agent film.
(4) An optical information medium according to the above (3) wherein said metal (including a semimetal) compound-containing layer formed in contact with said thin layer comprises an active energy beam-curable resin containing particles of a metal compound selected from a metal (including semimetal) chalcogenide, a metal (including semimetal) nitride, and a metal (including semimetal) carbide; and said metal compound particle has an average particle size of up to 500 nm.
(5) An optical information medium according to the above (3) wherein said metal (including a semimetal) compound-containing layer formed in contact with said thin layer comprises a composition containing a hydrolyzable metal (including semimetal) compound.
(6) An optical information medium according to the above (3) wherein said metal (including a semimetal) compound-containing layer formed in contact with said thin layer comprises a compound containing a poylsilazane.
(7) An optical information medium according to any one of the above (1) to (6) wherein the substituent R1 in formula (1) is a water- or oil-repellent fluorohydrocarbon substituent.
(8) An optical information medium according to any one of the above (1) to (7) wherein at least one of X, Y and Z in formula (1) is selected from a halogen, xe2x80x94OH, xe2x80x94OR2 (wherein R2 is an alkyl group), xe2x80x94OC(O)CH3, xe2x80x94NH2 and xe2x80x94Nxe2x95x90Cxe2x95x90O.
(9) An optical information medium according to any one of the above (1) to (8) wherein
said medium has a supporting substrate, and the recording and/or the reading is accomplished by irradiating a light beam from the side of said supporting substrate, and
said silane coupling agent film is formed on the side of the light beam incidence.
(10) An optical information medium according to the above (9) wherein
said optical information medium is a magneto-optical disk used by magnetic field modulation process which has a recording layer formed on the supporting substrate, wherein the recording and the reading is accomplished by irradiating a light beam from the side of said supporting substrate, and wherein a magnetic head is run on the side of said recording layer, and
said disk is coated with said silane coupling agent film on both the side of the light beam incidence and the side of the magnetic head.
(11) An optical information medium comprising a supporting substrate and a film layer formed on the supporting substrate to be optically recorded and/or read by a light beam irradiated from the side of said supporting substrate or said film layer, wherein
said medium is coated on the side of the light incidence with a thin layer having a thickness of up to 1 xcexcm comprising a metal (including a semimetal) compound selected from a metal (including semimetal) chalcogenide, a metal (including semimetal) nitride, and a metal (including semimetal) carbide, and
a metal (including a semimetal) compound-containing layer having a thickness thicker than said thin layer is formed in contact with said thin layer and on the side opposite to the side of the light incidence.
(12) An optical information medium comprising a supporting substrate and a film layer formed on the supporting substrate to be optically recorded and/or read by a light irradiated from the side of said supporting substrate or said film layer, wherein
said medium is coated on the side of the light incidence with a thin layer having a thickness of up to 1 xcexcm comprising hard carbon (diamond like carbon), and
a metal (including a semimetal) compound-containing layer having a thickness thicker than said thin layer formed in contact with said thin layer and on the side opposite to the side of the light incidence.
(13) An optical information medium according to the above (11) or (12) wherein said metal (including a semimetal) compound-containing layer formed in contact with said thin layer comprises an active energy beam-curable resin containing particles of a metal compound selected from a metal (including semimetal) chalcogenide, a metal (including semimetal) nitride, and a metal (including semimetal) carbide; and said metal compound particle has an average particle size of up to 500 nm.
(14) An optical information medium according to the above (11) or (12) wherein said metal (including a semimetal) compound-containing layer formed in contact with said thin layer comprises a composition containing a hydrolyzable metal (including semimetal) compound.
(15) An optical information medium according to the above (11) or (12) wherein said metal (including a semimetal) compound-containing layer formed in contact with said thin layer comprises a compound containing a polysilazane.
(16) An optical information medium comprising a supporting substrate and a film layer formed on the supporting substrate which is optically recorded and/or read by irradiating a light beam from the side of said supporting substrate or said film layer, wherein
said medium is formed on the side of the light incidence with a light-transmitting layer; and at least a part of said light-transmitting layer comprises an active energy beam-curable resin containing particles of a metal compound selected from a metal (including semimetal) chalcogenide, a metal (including semimetal) nitride, and a metal (including semimetal) carbide; and said metal compound particle has an average particle size of up to 500 nm.
(17) An optical information medium according to any one of the above (4), (13), or (16) wherein said metal compound particle is a metal chalcogenide particle.
(18) An optical information medium according to any one of the above (2), (4), (13), or (17) wherein said metal chalcogenide particle is silica particle.